Don't dispatch to cudnn if it is not possible to make it 32bit by splitting batch dim (#31383)
Summary:
Also a step towards supporting 64bit indexing in convolution.
See also: https://github.com/pytorch/pytorch/pull/31379
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31383
Differential Revision: D19183443
Pulled By: ngimel
fbshipit-source-id: 0c2030fac147e629d7be0c29f0683ec2b3f28c71